HMX compositions and processes for their preparation

ABSTRACT

A process for making alpha-HMX comprises the steps of: 
     (a) combining phosphorus pentoxide and nitric acid at a temperature of about 0-25° C., forming a reaction mixture; and 
     (b) adding a compound having the formula:                    
     wherein R is straight chain or branched alkyl having 1-5 carbon atoms, to the reaction mixture, whereby a product comprising alpha-HMX is produced.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims benefit of U.S. provisional application60/135,970, filed on May 26, 1999.

FIELD OF THE INVENTION

The invention relates to processes for producing HMX(1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane), processes forproducing intermediates that can be used to produce HMX, and compoundsand compositions produced by various of these processes.

BACKGROUND OF THE INVENTION

HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane), also referred toas octogen or cyclotetramethylenetetranitramine, is a highly energeticmaterial that is useful in various explosives and propellants formilitary and non-military applications. HMX is recognized as one of themost powerful nitramine explosives, and is used as the benchmark for allother explosives.

HMX is known to exist in four different crystal structures orpolymorphic forms—alpha, beta, gamma and delta. Of these polymorphs, itwas long believed that the beta form was the least sensitive and moststable, and thus the beta polymorph has been the most widely used formof HMX. The alpha and gamma polymorphs have commonly been dismissed astoo dangerous for use due to greater sensitivity, and the deltapolymorph is so unstable that it is of no commercial significance.

Despite its superior energetic properties, HMX has not been widely usedas an explosive due to difficulties in large-scale production andexcessive manufacturing costs. The first known process for themanufacture of HMX, the Bachmann process, was developed in the 1940's.The Bachmann process involves nitrolysis of hexamine (also known ashexamethylenetetraamine) with a mixture of nitric acid and a largeexcess (e.g., 20-fold) of acetic anhydride. HMX is produced as aby-product or contaminant along with a greater amount of anotherexplosive, RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine). The Bachmannprocess typically provides yields of 80-84%, of which only about 10-40%is HMX, based on the methylene content of the feed. When fully optimizedfor HMX, the maximum reported yield of HMX per mole of hexamine feed isabout 64%. Due to the inefficiencies in the process, and the largeamounts of hazardous waste materials produced, it is not appropriate forlarge-scale industrial production.

Other synthetic routes for making HMX have been proposed, involvingvarious intermediates. One such intermediate that has been used toproduce HMX is DAPT(3,7-diacetyl-1,3,5,7-tetraazabicyclo-[3.3.1]-nonane). DAPT is generallymade by reaction of wet hexamine and acetic anhydride. One problemcommon to all methods of manufacturing DAPT is the massive amount ofheat generated by the reaction. Because DAPT in solution will decomposerapidly at temperatures ranging from about 20-120° C., depending on pH,it is necessary to remove heat from the reaction mixture and thus keepthe temperature low. In effect, the rate of DAPT production is typicallylimited by the capacity of the reaction apparatus to withdraw heat bymeans of heat exchangers or the like. Due to the extremely exothermicnature of this reaction, in practice the rate of addition of aceticanhydride to the hexamine has been kept very low, so the rate of heatgeneration is kept at manageable levels. As a result, the time requiredto synthesize a given amount of DAPT is quite long, and the cost isrelatively high.

One method proposed for dealing with the tremendous amounts of heatgenerated by the reaction is to mix ice and water with hexamine tocreate a slurry, and then add acetic anhydride to the slurry.(Lukasavage U.S. Pat. No. 5,246,671.) Suitable temperatures for thisreaction slurry are described as ranging from −18° C. up to 120° C.

Another intermediate that can be used in the production of HMX is TAT(1,3,5,7-tetraacetyl-1,3,5,7-tetraazacyclooctane, also known as1,3,5,7-tetraacetyloctahydro-1,3,5,7-tetrazocine). TAT can be preparedby heating DAPT with acetic anhydride under anhydrous conditions, butthe yields from this process have been poor. Another process used toprepare TAT involves reacting DAPT with acetic anhydride, acetylchloride, and an alkanoic acid salt such as sodium acetate, underanhydrous conditions. (Siele U.S. Pat. No. 3,979,379.) However, thisprocess uses a large excess of acetic anhydride, thus making itrelatively expensive. Yet another process that has been used to make TATinvolves reacting DAPT with acetic anhydride in the presence of a metalacetate under anhydrous conditions at temperatures of 100-125° C.(Surapaneni U.S. Statutory Invention Registration H50.) However thereaction conditions and yield that have been reported for this processindicate that it is not economical for commercial use.

HMX can be synthesized by nitrolysis of TAT, using nitric acid anddinitrogen pentoxide or phosphorous pentoxide, at temperatures rangingfrom room temperature up to 40° C. (Lukasavage U.S. Pat. Nos. 5,124,493and 5,268,469.) This process too, however, has not seen acceptance on alarge production scale due to the economics involved.

SOLEX (1-(N)-acetyl-3,5,7-trinitro-cyclotetramethylenetetramine) isanother nitramine explosive, which is a byproduct of the nitration ofTAT to form HMX. SOLEX is relatively stable, having twice the impactresistance of RDX, is easily isolated, and can be produced using farless nitrating agent than is required for the direct preparation of HMXfrom TAT.

One process that has been described for the production of SOLEX involvesadding TAT to a solution of 98% nitric acid and phosphorus pentoxide ata temperature between 20-45° C. (Lukasavage U.S. Pat. No. 5,120,887.)The purity and product yields from this method are reported to bequantitative. Significantly, however, this method requires an excess ofnitrating agent, i.e., 7.5 grams of nitric acid per gram of TAT used,which makes the process relatively expensive. The SOLEX can be convertedto HMX by treatment with strong nitric acid.

Beta-HMX has been widely used as an explosive, despite the difficultiesand expense involved in its manufacture. One specific form that is soldis referred to as Class 5 beta-HMX (defined as particulate beta-HMX ofwhich 98% by weight will pass a 325 mesh (44 μm) sieve). Class 5beta-HMX can be sold for a higher price than coarser beta-HMX products,but is also more difficult to make. Usually it is made by first forminglarger beta-HMX particles, and then either grinding them in a waterslurry or “sand blasting” them against a hard surface, whereby thedesired finer beta-HMX particles are produced. This procedure istroublesome and relatively expensive.

Recently it was discovered that alpha-HMX can be produced that exhibitsless sensitivity to impact than beta-HMX. (Lukasavage U.S. Pat. No.5,268,469.) Production of this polymorph at a reasonable cost on a largescale would be advantageous as it would be useful as a substitute forthe beta-HMX used in existing explosive formulations.

Another problem in the prior art involves making durable shaped articlesthat contain explosive materials. Such articles typically comprise bothan explosive substance and a binder, the latter giving the compositionthe physical characteristics needed to retain the desired shape.However, such binders or other additives dilute the explosive power.

A long-standing need exists for an improved process for making HMX, andimproved HMX compositions and articles that exhibit desirable stability,impact sensitivity, and explosive properties. A particular need existsfor an improved process for making alpha-HMX that is relativelyimpact-insensitive.

SUMMARY OF THE INVENTION

One aspect of the invention is a process for making a3,7-dialkanoyl-1,3,5,7-tetraazabicyclo-[3.3.1]-nonane. The processcomprises the steps of:

(a) dissolving hexamine in water, thereby forming a reaction mixturehaving a temperature of about 0-30° C. (preferably about 10-25° C., mostpreferably about room temperature (about 22° C.));

(b) cooling the reaction mixture to keep its temperature below about 20°C.; and

(c) adding to the reaction mixture an alkanoic acid anhydride having theformula (RCO)₂O, where R is straight chain or branched alkyl having 1-5carbon atoms, whereby a product solution comprising a compound havingthe formula:

is produced, and wherein R is as defined above. Preferably in step (b),the reaction mixture is cooled to a temperature between about −30 and10° C., more preferably between about −15 and 5° C., most preferably ator below about 0° C.

In one preferred embodiment of this process, the alkanoic acid anhydrideis acetic anhydride and the product solution comprises DAPT. It ispreferred to use about 2.0-2.5 moles of acetic anhydride per mole ofhexamine, most preferably about 2.0-2.1 moles of acetic anhydride permole of hexamine.

One preferred way of cooling the reaction mixture is to use an externalcooling jacket through which a heat transfer fluid flows. Another way ofcooling the reaction mixture involves the addition of ice (e.g., atleast about 0.2 g of ice per g of hexamine). It is preferred to addabout 0.2-5.0 grams of ice to the reaction mixture per gram of hexamine(more preferably about 0.2-1.0, most preferably about 0.5), and to useabout 0.5-1.5 grams of water in step (a) per gram of hexamine (mostpreferably about 1.0 gram of water per gram of hexamine).

The ice preferably is present in an amount sufficient to maintain thetemperature of the reaction mixture at a temperature between about −30°C. and about 10° C., more preferably in an amount sufficient to maintainthe temperature of the reaction mixture at between about −15° C. andabout 5° C., most preferably at or below about 0° C. The ice can be usedin any of a variety of forms, such as crushed ice, shaved ice, blockice, and mixtures of ice and water.

Optionally, at least some of the ice or other device to provide coolingcan be enclosed in a container that prevents physical contact between itand the reaction mixture, but permits heat transfer with the reactionmixture. For example, the container can be a flexible bag made of one ormore thermoplastic polymers, or a rigid enclosure made of one or morethermoplastic or thermosetting polymers.

As another option, the ice can be pre-cooled to a temperature belowabout 0° C. before being added to the reaction mixture, preferably to atemperature below about −10° C., most preferably to below about −30° C.

As alternatives to an external cooling jacket or addition of ice,cooling of the reaction mixture can be provided by cooling coils havinga heat transfer fluid flowing therethrough, thermal control rods, andthe like.

The product solution in this process will typically comprise somevolatile compounds. One method of removing such volatile compoundscomprises the further steps of:

(d) heating the solution to at least about 40° C. and contacting thesolution with a flow of air that is substantially saturated with watervapor; and

(e) when about 50-80% by weight of the product solution has beenevaporated, heating the solution to about 70-150° C. and continuing tocontact the solution with a flow of air.

The pH of the product solution preferably is maintained above about 6.5during steps (d) and (e), more preferably above about 7.0. In apreferred embodiment of these purification steps, the product solutionis heated to about 40-45° C. in step (d), and to about 130-140° C. instep (e).

Another way of removing such volatile compounds comprises the additionalsteps of (d) feeding a liquid stream that comprises the product solutioninto the upper half of a stripper column; (e) feeding a gas streamhaving a temperature of at least about 120° C. into the lower half ofthe stripper column, whereby the gas stream and the liquid stream comeinto countercurrent contact in the stripper column; (f) withdrawing astream comprising the compound having the formula (I) from the bottom ofthe stripper column; and (g) withdrawing a waste stream comprising airand one or more of water vapor, water, formaldehyde, and acetic acid,from the top of the column. In one embodiment, the temperature of thegas stream is about 120-130° C. In other embodiments, the temperature ofthe gas stream is greater than about 150° C., or even greater than about200° C. Preferably the gas stream consists essentially of air, and thestripper column comprises packing.

This method of removing the volatile compounds can be considered toprovide thermal dissociation of the DAPT salt (e.g., DAPT acetate) thatenters the upper part of the stripper column, thereby forming an acidand a base. The stripper column can optionally be operated at reduced(e.g., sub-atmospheric) pressure and temperature.

One particularly preferred embodiment of this process can be used tomake DAPT, and comprises the steps of:

(a) dissolving hexamine in water, at a ratio of about 1.0 gram of waterper gram of hexamine, at a temperature of about 10-30° C., therebyforming a reaction mixture;

(b) adding ice to the reaction mixture in an amount sufficient tomaintain the reaction mixture at or below about 0° C.;

(c) adding about 2.0-2.1 moles of acetic anhydride per mole of hexamineto the reaction mixture, whereby a product solution comprising DAPT andvolatile compounds is produced;

(d) feeding a liquid stream that comprises the product solution into theupper half of a stripper column;

(e) feeding a gas stream having a temperature of at least about 120° C.into the lower half of the stripper column, whereby the gas stream andthe liquid stream come into countercurrent contact in the strippercolumn;

(f) withdrawing a stream comprising the compound having the formula (I)from the bottom of the stripper column; and

(g) withdrawing a waste stream comprising air and one or more of watervapor, water, formaldehyde, and acetic acid, from the top of the column.

The various embodiments of the above-described process can be operatedsafely with much greater throughput than prior processes. This processis especially valuable for producing DAPT. The increased production ratepossible with this process significantly reduces the cost of producingDAPT.

A second aspect of the invention is a process for making a1,3,5,7-tetraalkanoyl-1,3,5,7-tetraazacyclooctane. This processcomprises the steps of:

(a) reacting a compound having the formula:

wherein R is straight chain or branched alkyl having 1-5 carbon atoms,with an alkanoic acid anhydride having the formula (RCO)₂O, where R isas defined above, or an alkanoic acid halide (such as acetyl chloride)having the formula RC(O)X, where R is as defined above and X is halide,thereby producing a compound having the formula:

wherein R is as defined above; and

(b) reacting the compound having the formula (II) with the alkanoic acidanhydride in the presence of water and a catalytic amount of at leastone transition metal oxide, thereby producing a compound having theformula:

where R is as defined above.

In a preferred embodiment of this process, each R group is methyl, thealkanoic acid anhydride is acetic anhydride, and the product of step (b)comprises TAT. It is also preferred to use transition metal oxidecatalysts selected from the group consisting of copper oxides, ironoxides, and mixtures thereof.

Preferably about 2.0-2.5 moles of alkanoic acid anhydride are used permole of the compound having the formula (I), more preferably about2.0-2.2 moles of alkanoic acid anhydride per mole of that compound. Itis also preferred to use about 1.0-3.0 moles of water per mole of thecompound having the formula (II).

Step (a) preferably is performed at a temperature below about 138° C.Most preferably, step (a) is performed at a temperature of about110-120° C., and subsequently the temperature is raised to about130-140° C. for a time sufficient to evaporate residual water, alkanoicacid anhydride, and other volatile compounds.

One specific embodiment of this process makes TAT, and comprises thesteps of:

(a) reacting DAPT with acetic anhydride, thereby producing a compoundhaving the formula:

wherein R is methyl; and

(b) reacting the compound having the formula (II) with acetic anhydridein the presence of water and a catalytic amount of at least onetransition metal oxide, thereby producing TAT.

Another embodiment is a process for making TAT that comprises the stepsof the steps of: (a) reacting DAPT with acetic anhydride; and (b)reacting the product of step (a) with acetic anhydride in the presenceof a catalytic amount of at least one transition metal oxide. Preferablythe product of step (b) comprises TAT, and the process also includes thestep of reacting TAT with nitric acid and either phosphorus pentoxide ordinitrogen pentoxide, thereby forming HMX.

This process requires much less anhydride than prior processes, andtherefore is more cost-effective.

A third aspect of the invention relates to a novel intermediate that canbe used to make HMX, and a process for making that intermediate.

The novel intermediate is a compound having the formula:

wherein R is straight chain or branched alkyl having 1-5 carbon atoms.One such compound is 1-acetyl,5-acetate hexamethylene tetraamine (AAHT).

A process for making such an alkanoyl alkanoate hexamethylene tetraaminecomprises the step of:

(a) adding an alkanoic acid anhydride having the formula (RCO)₂O, whereR is straight chain or branched alkyl having 1-5 carbon atoms, to aslurry of hexamine and water, the slurry having a temperature betweenabout −78° C. and about 0° C., whereby an alkanoyl alkanoatehexamethylene tetraamine is produced.

In the presently preferred embodiment of this process, R is methyl, thealkanoic acid anhydride is acetic anhydride and the alkanoyl alkanoatehexamethylene tetraamine is AAHT.

In one embodiment, the slurry can further comprise ice. It is preferredthat the temperature of the slurry of hexamine, ice, and water isbetween about −50° C. and about −10° C., most preferably no higher thanabout −30° C. Preferably about 1.0-2.5 moles of alkanoic acid anhydrideare added per mole of hexamine, most preferably about 1.0-2.2 moles ofalkanoic acid anhydride per mole of hexamine.

The slurry of hexamine, ice, and water can suitably be formed bydissolving hexamine in water, and subsequently adding ice in an amountsufficient to lower the temperature of the slurry to at least about −10°C. Preferably the ice is added in an amount sufficient to lower thetemperature of the slurry to at least about −30° C. Optionally the icecan be pre-cooled to at least about −30° C. prior to being added to thehexamine and water. Preferably the slurry comprises about 1-5 grams ofhexamine per gram of ice, most preferably about 3 grams of hexamine pergram of ice.

One specific embodiment is a process for making AAHT that comprises thesteps of:

(a) dissolving hexamine in water, thereby forming a hexamine solution;

(b) forming a slurry of hexamine, ice, and water by adding ice that hasbeen pre-cooled to at least about −30° C. to the hexamine solution, theice being added in an amount sufficient to lower the temperature of theslurry to at least about −10° C.; and

(c) adding acetic anhydride to the slurry of hexamine, ice, and water,whereby AAHT is produced.

Another novel way of preparing an alkanoyl alkanoate hexamethylenetetraamine comprises the steps of:

(a) combining hexamine with water in a ratio of at least six moles ofwater per mole of hexamine, thereby forming an aqueous mixturecomprising hexamine hexahydrate;

(b) cooling the mixture to at least about −10° C.;

(c) adding to the mixture an alkanoic acid anhydride having the formula(RCO)₂O,

where R is straight chain or branched alkyl having 1-5 carbon atoms,with the mixture being at a temperature of −10° C. or lower, therebyproducing an alkanoyl alkanoate hexamethylene tetraamine.

As indicated above, preferably the alkanoic acid anhydride is aceticanhydride and the alkanoyl alkanoate hexamethylene tetraamine is AAHT.It is also preferred that the aqueous mixture is at or below about −30°C. in step (b), most preferably by addition of ice pre-cooled to atemperature below about −30° C. This process can suitably use about2.0-2.5 moles of alkanoic acid anhydride per mole of hexamine, mostpreferably about 2.0-2.2 moles of alkanoic acid anhydride per mole ofhexamine. Optionally, the anhydride can be pre-cooled to at least about−30° C. prior to its addition.

One specific embodiment of this second way of making AAHT comprises thesteps of:

(a) combining hexamine with water in a ratio of at least six moles ofwater per mole of hexamine, thereby forming an aqueous mixture;

(b) cooling the mixture to at least about −10° C., thereby forminghexamine hexahydrate; and

(c) adding to the mixture acetic anhydride that has been pre-cooled toat least about −30° C. prior to its addition, whereby the temperature ofthe mixture is kept at −10° C. or lower, thereby producing AAHT.

A fourth aspect of the invention relates todialkanoyl,dialkanoate-1,3,5,7-tetraazacyclooctane compounds, whereinthe alkanoyl groups each have 2-6 carbon atoms and the alkanoate groupseach have 3-8 carbon atoms. For example, such compounds can have theformula:

wherein R is straight chain or branched alkyl having 1-5 carbon atoms.Alternatively, two R groups can be linked as part of a bidentatepolymeric moiety. In one preferred compound in this class, R is methyl.

This aspect of the invention also relates to a process for making such a1,3,5,7-tetraalkanoyl-1,3,5,7-tetraazacyclooctane compound, comprisingthe steps of:

(a) reacting a compound having the formula:

wherein R is straight chain or branched alkyl having 1-5 carbon atoms,with an alkanoic acid anhydride having the formula (RCO)₂O, where R isstraight chain or branched alkyl having 1-5 carbon atoms, at atemperature greater than about 50° C., thereby forming a compound havingthe formula:

wherein R is as defined above; and

(b) contacting the compound having the formula (V) with water in thepresence of a catalytic amount of at least one transition metal oxide,thereby producing a compound having the formula:

wherein R is as defined above. As before, preferably the alkanoic acidanhydride is acetic anhydride, and the product of step (b) comprisesTAT.

Preferably the reaction of step (a) takes place at a temperature of atleast about 100° C., most preferably at about 110-120° C. The presentlypreferred transition metal oxide catalysts are copper oxides, ironoxides, or mixtures thereof. It is also preferred to use about 2-4 molesof alkanoic acid anhydride per mole of compound having the formula (IV).

One specific embodiment of this process comprises the steps of: (a)reacting AAHT with acetic anhydride at a temperature greater than about50° C.; and (b) contacting the product of step (a) with water in thepresence of a catalytic amount of at least one transition metal oxide.

Another embodiment comprises the steps of: (a) reacting AAHT with aceticanhydride at a temperature greater than about 100° C., thereby formingthe diester derivative of AAHT; and (b) reacting the diester with waterin the presence of a catalytic amount of at least one transition metaloxide, thereby producing TAT.

Although one desirable use of this process is to make the diester (i.e.,a dialkanoyl, dialkanoate-1,3,5,7-tetraazacyclooctane) for use in makingTAT or an analog thereof, it is also possible to stop the process at thepoint at which the diester has been formed and recover it.

Among the advantages of this process is that the reaction can be carriedout at much lower temperatures than those required for making TAT fromDAPT. The reduction in temperature increases the yield as well as thesafety of the process.

A fifth aspect of the invention is a process for making a1-(N)-alkanoyl-3,5,7-trinitro-cyclotetramethylenetetramine compound.This process comprises the steps of:

(a) combining a compound having the formula:

wherein R is straight chain or branched alkyl having 1-5 carbon atoms,with nitric acid at a temperature between about 15-50° C., therebyproducing a reaction mixture; and

(b) adding phosphorus pentoxide to the reaction mixture, whereby acompound having the formula:

is formed, wherein R is as defined above.

As stated above, preferably each R group is methyl, and thus the productis SOLEX. The temperature in step (a) preferably is between about 20-40°C., most preferably about 20-30° C. It is also preferred that the weightratio of nitric acid to the compound having the formula (III) is betweenabout 0.5:1 to about 5:1, most preferably about 1.5:1. (Preferred weightratios are given for the embodiment where R is methyl. The preferredweight ratio would change if R was changed.) Preferably the weight ratioof phosphorus pentoxide to the compound having the formula (III) is nogreater than about 1:1, more preferably no greater than about 0.75:1,most preferably no greater than about 0.5:1.

The rate of reaction can be controlled by controlling the rate ofaddition of phosphorus pentoxide to the reaction mixture, or (lessdesirably) by applying external cooling to the reaction mixture. Ineither method, control can be in response to measurements of thetemperature of the reaction mixture. The extent of the nitration of thecompound having the formula (III) can be controlled by using a molarexcess of that compound. The extent of the excess of compound (III)limits the extent of the conversion.

One specific embodiment of this process produces SOLEX and comprises thesteps of:

(a) combining TAT with nitric acid at a temperature between about 10-15°C., thereby producing a reaction mixture; and

(b) adding phosphorus pentoxide to the reaction mixture at a controlledrate, whereby SOLEX is formed.

This process requires much less phosphorus pentoxide than prior methodsof making SOLEX. This aspect of the invention takes advantage of thefact that SOLEX is relatively stable, (having twice the impactresistance of RDX), is easily isolated, and can be produced using a farsmaller amount of nitrating agent than is required for the directpreparation of HMX from TAT. Further, SOLEX can be readily convertedinto alpha-HMX, as described below.

Another way of making such a1-(N)-alkanoyl-3,5,7-trinitrocyclotetramethylenetetramine compoundcomprises the steps of:

(a) combining nitric acid and phosphorus pentoxide, thereby producing areaction mixture; and

(b) adding to the reaction mixture a compound having the formula:

wherein R is straight chain or branched alkyl having 1-5 carbon atoms;wherein the reaction mixture is kept at temperature no greater thanabout 68° C.; and whereby a compound having the formula:

is formed, wherein R is as defined above.

In one preferred embodiment of this process, each R group is methyl, andthus the compound having the formula (VI) is SOLEX. Preferably theweight ratio of nitric acid to phosphorus pentoxide in step (a) is fromabout 2:1 to about 4:1, more preferably about 3:1. The weight ratio ofnitric acid to the compound having formula (III) preferably is fromabout 1.5:1 to about 3.0:1, and the weight ratio of phosphorus pentoxideto the compound having formula (III) preferably is from about 0.5:1 toabout 0.75:1.

It is also preferred that the temperature of the reaction mixture instep (a) is about 0-30° C., and that the temperature of the reactionmixture is allowed to rise no higher than about 40-68° C., morepreferably no higher than about 45-55° C.

Another embodiment is a process for nitrating TAT comprising the stepsof (a) combining TAT and nitric acid to form a reaction mixture having atemperature of about 15-50° C.; and (b) adding P₂O₅ to the reactionmixture. The product of step (b) can comprise HMX, SOLEX, or a mixturethereof. The product preferably has a melting point of about 260-281°C., more preferably about 270-281° C. The extent of the nitration, i.e.,whether the conversion stops at SOLEX, or produces a mixture of SOLEXand HMX, or pure HMX, can be controlled by using a molar excess of TAT.

A sixth aspect of the invention is a process for making HMX. Oneembodiment of the invention produces alpha-HMX, and, comprises the stepsof:

(a) combining phosphorus pentoxide and nitric acid at a temperature ofabout 0-25° C., forming a reaction mixture; and

(b) adding a compound having the formula:

wherein R is straight chain or branched alkyl having 1-5 carbon atoms,to the reaction mixture, whereby a product comprising alpha-HMX isproduced. This reaction is preferably a solid-state nitration reaction,i.e. the SOLEX reacts while still a solid rather than being dissolved inthe nitric acid. In one preferred embodiment of this process, thecompound having the formula (VI) is SOLEX.

Preferably the temperature in step (a) is about 10-20° C., mostpreferably about 15° C. It is also preferred that the nitric acid has aconcentration of at least about 98% by weight.

The HMX produced by this process is at least 99% by weight alpha-HMX,often essentially 100% alpha-HMX. Further, the yield of alpha-HMX istypically at least 99%.

One specific embodiment of this process for making alpha-HMX comprisesthe steps of:

(a) adding phosphorus pentoxide to nitric acid at a temperature of about0-25° C., forming a reaction mixture; and

(b) adding SOLEX to the reaction mixture, whereby a solid-statenitration reaction produces alpha-HMX.

The invention also relates to the alpha-HMX product made by theabove-described process. This product is extremely pure alpha-HMX, e.g.,essentially no RDX or beta-HMX contamination. For example, the productcan be 99 weight % or more alpha-HMX. In a preferred embodiment, theproduct comprises less than 0.01% by weight RDX, more preferably no RDXwhatsoever. The majority by weight (i.e., greater than 50% by weight) ofthe alpha-HMX particles produced by this process have the form of longfibers. A majority by weight of these alpha-HMX fibers have an aspectratio (length:diameter) of at least about 50:1, sometimes as great as atleast about 100:1 or even 1,000:1.

The alpha-HMX can be made into long fibers by dissolving the alpha-HMXin boiling aqueous solution (e.g., in pure water), and then cooling thesolution below the boiling point. These steps form fibrous alpha-HMX. Inone embodiment, the majority by weight of the alpha-HMX produced uponcooling is fibers having an aspect ratio (length:diameter) of at leastabout 50:1, more preferably at least about 100:1, most preferably atleast about 1,000:1. In particular, the product of these steps willtypically be a mass comprising a plurality of such fibers. This materialcan be pressed or otherwise shaped into useful articles.

In one embodiment, the product is an equilibrium mixture, as describedabove, of alpha-HMX (making up by far the majority of the product) andSOLEX (making up a very small percentage, usually much less than 1% ofthe product).

Preparing alpha-HMX by the synthetic route that goes through SOLEX helpscontrol the polymorphic form of the product, permitting the manufactureof pure (or very nearly pure) alpha-HMX at essentially quantitativeyield.

Another way of making an HMX composition comprises the steps of:

(a) combining a compound having the formula:

wherein R is straight chain or branched alkyl having 1-5 carbon atoms,with nitric acid, thereby forming a reaction mixture; and

(b) adding phosphorus pentoxide to the reaction mixture, whereby aproduct that comprises HMX is produced. The compound (VI) preferably isdissolved in nitric acid and the reaction takes place in solution. TheHMX produced in this way can be converted easily to beta-HMX bycontacting it with an organic solvent, e.g., heated acetone. Thisprovides a less expensive method of manufacturing beta-HMX than theconventional direct synthesis methods.

In one preferred embodiment of this method, the compound having theformula (VI) is SOLEX. In another embodiment, the product of step (b)comprises an equilibrium mixture of alpha-HMX and SOLEX. The meltingpoint of the product of step (b) preferably is at least about 277° C.(All melting points given herein are as determined by capillarymethodology.)

When the R group is methyl (i.e., the group pendant from the N isacetyl) it is preferred that the weight ratio of nitric acid to SOLEX instep (a) is from about 1.5 to about 3.0, more preferably about 1.8. Itis also preferred that the weight ratio of phosphorus pentoxide to thecompound having the formula (VI) is from about 0.25 to about 2.0, morepreferably about 0.7-0.8. The product made by the above-describedprocess comprises HMX. Without being bound by theory, the HMX made bythis particular process may be a form of alpha-HMX, or it may be adifferent polymorphic form of HMX. As long as the product's meltingpoint is at least about 277° C., it can easily be converted to highlypure beta-HMX by contacting the product with a hot organic solvent(e.g., acetone at a temperature of 40-100° C., preferably about 56° C.).

In any of these embodiments of the process, when the nitration reactionhas proceeded to the desired extent, the reaction can be stopped bycooling the reaction mixture (e.g., by adding ice). Optionally, aprocess of making HMX as described above can further comprise thefollowing back-end steps:

(c) filtering the product of step (b), whereby alpha-HMX is retained bya filter and an impurity-containing filtrate is collected;

(d) treating the filtrate with a source of ammonium ions to adjust itspH to about 4.0-5.0;

(e) evaporating water from the filtrate; and

(f) cooling the filtrate sufficiently to crystallize ammonium nitratecrystals.

These additional steps produce a highly pure ammonium nitrate byproduct,which can be sold for use in fertilizer or the like. Thus, theseadditional steps enhance the economics of the process by reducing theamount of waste material that must be disposed of and creating avaluable byproduct. In these steps, preferably the pH of the filtrate isadjusted to about 4.7 and the source of ammonium ions is ammonia.

Alternatively, instead of performing steps (c)-(f) after filtration toremove the solid product, the remaining nitric acid can be concentratedfor recycle.

A seventh aspect of the invention relates to compositions and articlesthat comprise HMX, as well as processes for making them.

One such composition comprises HMX particles (e.g., alpha-HMX particles)and at least one second material coated thereon and/or sorbed into voidsin the particles. The term “second material” is used herein to refergenerically to materials other than alpha-HMX which can be combined withalpha-HMX to form mixtures, granules, and/or shaped articles.Preferably, a majority by weight of the alpha-HMX particles are in theform of fibers, which may be porous (i.e., contain some void spaces).Typically a majority by weight of the alpha-HMX fibers have an aspectratio (length:diameter) of at least about 50:1, often as great as about1,000:1 or even higher.

A variety of second materials can be used in the invention, includingmixtures of two, three, or more different second materials. One suitableexample of a second material is an energetic material, such as beta-HMX,RDX, TNT, ammonium nitrate, or a mixture thereof. Another suitableexample of a second material is a fuel, such as aluminum, lithiumhydride, lithium aluminum hydride, or a mixture thereof. As anotherexample, a first set of particles can have coated and/or sorbed thereonone component of a binary explosive, and a second set of particles canhave coated and/or sorbed thereon the other component of the binaryexplosive (e.g., material comprising nitro moieties and glycerin). Whenthe two sets of particles are combined, a binary explosive compositioncan be formed.

Yet another suitable example of a second material is one that alters thestructural properties of the composition as compared to the structuralproperties of the alpha-HMX particles in the absence of the secondmaterial. For instance, the second material can be one that increasesthe durability, density, or structural strength of the composition, suchas carbon fibers or silicone molding resins. Another suitable example ofa second material is one or more polymerizable monomers, such ascaprolactam, or a mixture of adipic acid and hexamethylene diamine. Itis possible to polymerize such monomers in situ after they are coatedonto the alpha-HMX, thereby providing additional strength or otherdesirable properties. By coating a HMX particle with such monomers,forming a plurality of such articles into a granule or article, and thenpolymerizing the monomers in situ, an HMX-containing granule or articlecan be formed that also comprises a polymeric “cage” or framework.

It is also possible to use multiple layers of coatings comprising secondmaterials. For instance, the composition can comprise a plurality oflayers coated on the alpha-HMX particles, each layer comprising at leastone second material. The second material can be the same in each of theplurality of coated layers. Alternatively, at least two of the pluralityof coated layers comprise different second materials, or each coatedlayer can comprise a different second material.

This aspect of the invention also relates to durable alpha-HMXcontaining articles, comprising a plurality of particles, the particlescomprising alpha-HMX coated with at least one second material. A“durable article” in this context is one that will retain is shape undernormal handling.

In such an article, the plurality of coated alpha-HMX particles canoptionally comprise (a) a first group of alpha-HMX particles coated witha second material, and (b) a second group of alpha-HMX particles coatedwith a different second material. For example, the different secondmaterials could be ones that can be combined to firm a binary explosive.Then when the two groups (a) and (b) are combined, the overallcomposition is explosive.

The article can suitably be formed by pressing the plurality of coatedparticles into a shape, or by granulating a plurality of such particles,using techniques described below. The article can further comprise acoating of a second material on the exterior of the article, or even aplurality of coatings of one or more second materials on its exterior.As outlined above, the second material can be the same in each of theplurality of coatings, can be different in at least two of the coatings,or can be different in each coating.

In one particular embodiment, the article further comprises a coating onthe exterior of the article. This coating comprises alpha-HMX particlesthat have been coated with a second material. Alternatively, the articlecan comprise a plurality of coatings, each of which comprises alpha-HMXparticles that have been coated with a second material.

The article can also comprise a second material that has been sorbedinto the article, or onto an alpha-HMX particle. A process for sorbing asecond material onto alpha-HMX particles, comprises the steps of:

(a) providing at least one second material;

(b) mixing the second material with a liquid solvent;

(c) contacting the solvent with alpha-HMX particles; and

(d) evaporating the solvent, whereby the second material sorbs ontoand/or into the alpha-HMX particles.

The second material can initially be in a variety of forms (e.g., solidparticulates, liquid, or gas).

In one embodiment, the solvent of step (b) is an organic solvent, suchas acetone, cyclohexane, gamma butyrolactone, or a mixture of one ormore of these. This process can further comprise the step of forming agranule that itself comprises a plurality of the alpha-HMX particleshaving the second material coated on the particles. The granules andarticles formed as described above are highly stable, for exampleholding their structural integrity in boiling water or acetone.

The combination of materials involved in this aspect of the inventioncan achieve a higher level of energy per unit volume, thus making thecomposition highly desirable for use as an explosive or propellant.Depending on what secondary materials are used, the composition can alsohave its energetic properties per unit volume increased, or itsstructural strength, density, or durability increased. Theseenhancements are especially useful for making various explosive,propellant, and pyrophoric devices (e.g., shaped charges).

An eighth aspect of the invention is a process for making beta-HMX. Thiscan be accomplished by a process that comprises the steps of:

(a) combining a compound having the formula:

wherein R is straight chain or branched alkyl having 1-5 carbon atoms,with nitric acid, thereby forming a reaction mixture;

(b) adding phosphorus pentoxide to the reaction mixture, whereby aproduct that comprises HMX is produced;

(c) contacting the so-produced HMX with a solvent; and

(d) evaporating the solvent, whereby beta-HMX crystals are formed.

This aspect of the invention allows the manufacture of beta-HMX byconversion of a different form of HMX (e.g., alpha-HMX). The HMX used asthe starting material preferably is made by a process comprising thesteps of:

(a) combining a compound having the formula:

wherein R is straight chain or branched alkyl having 1-5 carbon atoms,with nitric acid, thereby forming a reaction mixture; and

(b) adding phosphorus pentoxide to the reaction mixture, whereby aproduct that comprises HMX is produced. The compound (VI) preferably isdissolved in nitric acid and the reaction takes place in solution. Themelting point of the product of step (b) preferably is at least about277° C.

The conversion process comprises the steps of:

(a) contacting the so-produced HMX with a solvent;

(b) evaporating the solvent, whereby beta-HMX crystals are formed.

In one embodiment, the HMX is dissolved or suspended in the solvent instep (a). In a specific embodiment of the process, the solvent is anorganic solvent, such as acetone, cyclohexane, gamma butyrolactone, or amixture of one or more of these.

Optionally, seed crystals of beta-HMX can be added to the solvent tofacilitate crystallization. However, seed crystals are generally notrequired. If seed crystals are used, they can be provided, for example,by including no more than about 1% by weight (preferably no more thanabout 0.1%) beta-HMX in the HMX of step (a). If a small amount ofbeta-HMX byproduct is present in the starting HMX composition, it canserve this purpose. Alternatively, the beta-HMX crystals can provided byadding them to the solvent from an external source.

In one preferred embodiment of the process, the solvent is evaporated byspray drying. This spray drying can suitably take place at a temperatureof less than about 56° C., preferably at about 50° C. This process canproduced Class 5 beta-HMX, or even finer particles.

A ninth aspect of the invention is a process for forming alpha-HMXcontaining granules from at least one particulate material, comprisingthe steps of:

(a) selecting particulates having a particle size distribution; and

(b) fluidizing the particulates, whereby particulates agglomerate toform granules.

In one embodiment, this process involves accelerating the fluidizedparticulates against a solid surface, and more preferably, continuouslyimpacting such particulates against a surface, most preferably a curvedsurface. Vessels having circular cross-sections are well suited forperforming this operation. A rotating impeller, or alternatively a gasstream, can suitably be used to accelerate the particles.

Although this process is especially well-suited for producing granulesfrom alpha-HMX particles made as described above, it is not limited touse with that particular material. This process can be used with avariety of particulate materials, such as drugs and pharmaceuticalexcipients.

In one preferred embodiment, the fluidized particulates are impactedagainst a solid surface, for example by being circulated around acircular or elliptical path. Preferably, the particulates are circulatedin a channel in a vessel, whereby the motion creates centrifugal forcethat impacts the particulates against the solid surface of the channel,whereby a granule is formed that tumbles as it continues to circulatearound the channel.

The particle size distribution in step (a) can be any desired range,including taking particulate alpha-HMX and using it as-is.Alternatively, a particle size distribution can be cut from the initialmaterial, for example by sieving.

Optionally, a small amount of an organic solvent (e.g., about 0.001-0.5g of organic solvent per g of alpha-HMX or other particulate material,more preferably about 0.05-0.1 g of solvent per g of particulates) canbe added to the particulates. This small amount of solvent helpsfluidize the particles, and facilitates formation of a granule, but doesnot dissolve a large percentage of the alpha-HMX, which could cause theeventual formation of a different polymorph.

Fluidization of the particles can be achieved, for example, by placingthem in high velocity gas streams (e.g., “sand-blasting”). The densityof the resulting granules can be controlled by selecting the amount ofkinetic energy imparted to the particles in step (b). In other words,the greater the velocity of the gas steam(s) in which the particles arefluidized, the denser the resulting granules will be.

Optionally, the alpha-HMX particulates can be coated and/or impregnatedwith one or more second materials, as described above, such as energeticmaterials or fuels. If one or more of the second materials comprisepolymerizable monomers, the process can optionally further comprise thestep of polymerizing those monomers in situ, either before or after thegranule is formed.

In one particular embodiment, a second material is sorbed onto thealpha-HMX particles by a process comprising the steps of:

(a) providing at least one second material;

(b) mixing the second material with a liquid solvent;

(c) contacting the solvent with alpha-HMX particles; and

(d) evaporating the solvent, whereby the second material adsorbs ontothe alpha-HMX particles

This aspect of the invention also relates to a durable article thatconsists essentially of alpha-HMX and at least one second material. Inother words, this article need not comprise any binder; the propertiesof the alpha-HMX particles allow them to be formed into a durablearticle in a mixture with the second material, without requiring theinclusion of a material with adhesive properties. Optionally, such anarticle can comprise no more than about 2% by weight graphite, tofacilitate manufacturing the article.

The second materials included in such an article can be varied, asdescribed above. One particularly useful second material in this aspectof the invention is aluminum in particulate form. One particularembodiment of the invention is an article as described above thatcomprises about 0.1-20% by weight aluminum. One especially usefulembodiment is a durable article that consists of alpha-HMX and about0.1-20% by weight aluminum.

This aspect of the invention also relates to a process for making analpha-HMX composition, comprising the steps of:

(a) mixing particulate alpha-HMX and at least one particulate materialselected from the group consisting of energetic materials and fuels,thereby forming a particulate mixture;

(b) fluidizing the particulate mixture; and

(c) impacting the particulate mixture against a solid surface, wherebythe particulates in the mixture agglomerate to form granules.

As mentioned above, the particulate mixture can be circulated around acircular or elliptical path, for example in a channel in a rotatingvessel.

The granules formed from alpha-HMX particles will typically contain voidspaces. Therefore, the process can optionally further comprise the stepof sorbing a second material into the granules. This can be done byusing a vacuum to a gas phase that comprises draw the second materialinto the granule. Alternatively, this can be done by:

(d) mixing the second material with a liquid solvent (e.g., an organicsolvent);

(e) contacting the solvent with the granules; and

(f) evaporating the solvent, whereby the second material is sorbed intothe granules.

These granules will retain their solid, durable character, even withlarge amounts of secondary materials added, for example even if theycontain as much as 90% by weight TNT, and even at temperatures greaterthan 200° C. Further, the granules are pressable, for example to makeexplosive devices (e.g., shaped charges). In addition, the compositiondoes not tend to build up static electrical charges. Typically, thegranules into whose void spaces a second material has been sorbed willhave greater bulk density than the granule in the absence of the sorbedsecond material.

A tenth aspect of the invention is a process for preparing an HMXproduct, comprising the steps of:

(a) providing a granule that comprises a plurality of alpha-HMXparticles and which has internal void spaces; and

(b) sorbing at least one second material into the void spaces in thegranule.

The term “HMX product” is used herein to refer generically tocompositions that comprise HMX and one or more second materials thathave been coated onto and/or sorbed into an alpha-HMX particle, granule,or article. (“Granule” as used herein generally refers to an object thatcomprises a plurality of particles, while “article” refers to arelatively large object formed into a desired shape that is large enoughto be easily visible to the naked eye).

The second material can be sorbed into the granules by using a vacuum todraw a gas phase comprising the second material into the granule.Alternatively, the second material can be sorbed into the granules by:

(c) mixing the second material with a liquid solvent (e.g., an organicsolvent);

(d) contacting the solvent with the granules; and

(e) evaporating the solvent, whereby the second material is sorbed intothe granules.

Various second materials can be used, as explained above. Suitableexamples include energetic materials and fuels.

The process can optionally further comprise coating the exterior of thegranule with a second material. This second material coated on theexterior of the granule can be the same as the second material sorbedinto the granule, or it can be different. As another option, a pluralityof coatings can be applied to the exterior of the granule. As yetanother option, a mixture of at least two second materials can be sorbedinto the granule.

This aspect of the invention also relates to a process for preparing anHMX product, comprising the steps of:

(a) contacting alpha-HMX granules having void spaces therein with ansolvent in an amount from about 0.1-2.5 g of solvent per g of alpha-HMX,whereby a fraction of the HMX is dissolved;

(b) providing beta-HMX crystals in the dissolved HMX; and

(c) evaporating the solvent, whereby beta-HMX is deposited in voidspaces of undissolved alpha-HMX particles.

The solvent can suitably be an organic solvent, for example selectedfrom the group consisting of acetone, cyclohexane, gamma butyrolactone,and mixtures thereof. The beta-HMX crystals can be provided as part ofthe alpha-HMX granules. If the goal is to fill void spaces in thealpha-HM granules with beta-HMX, then preferably the beta-HMX crystalscomprise less than 1% by weight of the alpha-HMX granules, morepreferably less than 0.1%. Alternatively, the beta-HMX crystals can beproviding by adding them to the solvent from an external source. Eitherway, it is preferred that the amount of beta-HMX crystals provided instep (b) is no greater than about 1.0% by weight of the alpha-HMX, morepreferably no greater than about 0.1% by weight of the alpha-HMX.

Alternatively, if the goal is to produce a granule or article comprisingprimarily beta-HMX, then the weight ratio of beta to alpha-HMX can be ashigh as desired (e.g., 1:1 or higher). The relatively small amount ofalpha-HMX in this embodiment can serve to bind the beta-HMX particlestogether as a granule or article.

The amount of solvent used should be small enough so that only a minorportion of the alpha-HMX is dissolved. Preferably about 10-20% by weightof the alpha-HMX is dissolved in step (a).

The process can further comprise the step of pressing the product ofstep (c) into a shaped article.

The product produced by this aspect of the invention has greater bulkdensity than the original granules or article, due to the incorporationof a second material into the void spaces. If the second material is anenergetic material or a fuel, this enhances the overall energetic effectof the article or granule.

An eleventh aspect of the invention is a method of performing anexothermic chemical reaction, comprising the steps of:

(a) contacting reactants to form a liquid reaction mixture in an openreaction vessel, wherein:

(i) the reaction vessel has a closed bottom with a first diameter;

(ii) the reaction vessel has an open top with a second diameter that isgreater than the first diameter;

(iii) the reaction vessel has a wall that is connected to the bottom,the wall having an inner surface, at least a part of which contacts thereaction mixture; and

(iv) the reaction vessel comprises an adjustable stirrer in contact withthe reaction mixture; and

(b) controlling the temperature of the reaction mixture by adjusting thedegree of stirring of the reaction mixture by the adjustable stirrer,whereby the centrifugal force from the stirring causes the liquidreaction mixture to move upward along the inner surface of the reactionvessel. By placing the reaction mixture in physical contact with agreater surface area of the inner surface of the reaction vessel,cooling of the reaction mixture can be enhanced.

In one embodiment, the reaction vessel is frustoconical in shape. Oneembodiment of the adjustable stirrer comprises a rotatable impellerwhich is mounted on a shaft. The shaft is driven by a motor, and thuscan rotate the impeller about a vertical axis of the reaction vessel.The method can further comprise applying external cooling to thereaction vessel (for example, with an external jacket through which aheat transfer fluid flows). If the temperature of the reaction mixtureexceeds a target temperature, the speed of rotation of the impeller canbe increased. This increase in rotational speed will increase thecentrifugal force that tends to move the reaction mixture up the wallsof the vessel. By placing the reaction mixture in physical contact witha greater surface area inside the vessel, the rate of cooling isincreased, and the temperature of the reaction mixture can be decreased.

In the same way, if the temperature of the reaction mixture exceeds apredetermined alarm level, the speed of rotation of the impeller can beincreased sufficiently to cause a predetermined amount of the reactionmixture to be expelled from the reaction vessel through its open top,thereby bringing the remaining reaction mixture under thermal controland preventing catastrophic damage to the equipment from excessivereaction temperatures.

Although this method has wide applicability in exothermic reactions, itis particularly useful in one or more of the above-described processesin which a nitramine or nitramine intermediate is manufactured. Forexample, this method is useful where the reactants comprise hexamine andacetic anhydride; DAPT and acetic anhydride; TAT, nitric acid, andeither or both of phosphorus pentoxide or dinitrogen pentoxide; hexaminehexahydrate and acetic anhydride; AAHT and acetic anhydride; or SOLEX,nitric acid, and either or both of phosphorus pentoxide or dinitrogenpentoxide.

One specific embodiment of the invention is a method of performing anexothermic chemical reaction, comprising the steps of:

(a) contacting reactants to form a liquid reaction mixture in afrustoconical reaction vessel, wherein:

(i) the frustoconical reaction vessel has a closed bottom with a firstdiameter;

(ii) the frustoconical reaction vessel has an open top with a seconddiameter that is greater than the first diameter;

(iii) the frustoconical reaction vessel has a wall that is connected tothe bottom the wall having an inner surface, at least a part of whichcontacts the reaction mixture; and

(iv) the frustoconical reaction vessel comprising a motor-drivenimpeller which is rotatable about a vertical axis of the reactionvessel;

(b) mixing the reaction mixture in the frustoconical reaction vessel byrotating the impeller; and

(c) controlling the temperature of the reaction mixture by (1) applyingexternal cooling to the frustoconical reaction vessel and (2) adjustingthe speed of rotation of the impeller, whereby the centrifugal forcefrom rotation of the impeller causes the liquid reaction mixture to moveupward along the inner surface of the frustoconical reaction vessel;wherein when the temperature of the reaction mixture exceeds a targettemperature, the speed of rotation of the impeller is increased; andwherein when the temperature of the reaction mixture exceeds apredetermined level, the speed of rotation of the impeller is increasedsufficiently to cause a predetermined amount of the reaction mixture tobe expelled from the frustoconical reaction vessel through its open top.

This aspect of the invention also relates to chemical reaction apparatusthat comprises:

(a) an open reaction vessel comprising:

(i) a closed bottom having a first diameter;

(ii) an open top having a second diameter that is greater than the firstdiameter;

(iii) a wall that is connected to the bottom, the wall having an innersurface; and an outer surface; and

(b) an adjustable stirrer located within the vessel;

(c) a temperature sensor within the vessel; and

(d) a motor that is operationally connected to the adjustable stirrer,the motor being adjustable so as to change the rate of stirring inresponse to the temperature measure by the temperature sensor.

In one embodiment, the adjustable stirrer comprises an impeller mountedon a rotatable shaft, the impeller being located within the vessel andthe shaft extending from the impeller to the motor. The apparatus canfurther comprise a computer which adjusts the speed of the motor inresponse to the temperature measure by the temperature sensor.

This aspect of the invention provides an inexpensive, simple, and safemeans for performing exothermic reactions, such as those involved inproducing alpha-HMX and its various intermediates.

A twelfth aspect of the invention is a process for separating anitramine or nitramine intermediate (e.g., DAPT) from water and volatileorganic compounds, comprising the steps of:

(a) feeding a liquid stream comprising a liquid nitramine or nitramineintermediate (e.g., DAPT), water, and at least one volatile organiccompound, into the upper half of a stripper column;

(b) feeding a gas stream having a temperature of at least about 120° C.into the lower half of the stripper column, whereby the gas stream andthe liquid stream come into countercurrent contact in the strippercolumn;

(c) withdrawing a nitramine or nitramine intermediate stream from thebottom of the stripper column; and

(d) withdrawing a waste stream comprising gas and one or more of watervapor, water, formaldehyde, and acetic acid, from the top of the column.

The temperature of the gas stream can suitably be about 70-200° C. Inother embodiments of the process, the temperature of the gas stream isgreater than about 150° C., or even greater than about 200° C., and nosubstantial degradation of the nitramine or intermediate occurs, due tothe relatively short residence time of the compound in the column.

The gas stream preferably consists essentially of air (optionallycomprising some water vapor). It is also preferred that the strippercolumn comprises packing. The column can optionally be operated atbelow-atmospheric pressure, which would also change the temperature ofoperation.

This process is especially useful in the purification of a liquid streamthat comprises DAPT. Conventional filtration of such a stream is arelatively slow operation. Therefore, one particularly preferredembodiment is a process for separating DAPT from water and volatileorganic compounds, comprising the steps of:

(a) feeding a liquid stream comprising DAPT, water, and at least onevolatile organic compound, into the upper half of a stripper column;

(b) feeding an air stream having a temperature of at least about 120° C.into the lower half of the stripper column, whereby the gas stream andthe liquid stream come into countercurrent contact in the strippercolumn;

(c) withdrawing a DAPT stream from the bottom of the stripper column;and

(d) withdrawing a waste stream comprising air, water vapor,formaldehyde, and acetic acid, from the top of the column.

Preferably the DAPT stream in step (c) comprises no more than about 5%water by weight.

The various aspects of the present invention have numerous advantagesover the prior art. One of the most significant advantages isconsiderably lower cost than prior art methods for making alpha-HMX, inpart due to the use of lower temperatures and less reactants. Inparticular, the synthetic routes of the present invention make possiblea five-fold reduction in the cost of manufacturing HMX. The alpha-HMXproduced by the methods of the present invention is exceptionally pure,which enhances its performance as an explosive or rocket propellant.Another advantage of the present invention is the ease of manipulationof the final product to modify its properties, for example bycombination with other materials, or by pressing into shaped articles,such as shaped charges.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photomicrograph of alpha-HMX particles produced by a processin accordance with the present invention. The white bar at the bottom ofthe photograph represents a length of 11.1 microns.

FIG. 2 is a photomicrograph of alpha-HMX particles produced by a priorart process. The white bar at the bottom of the photograph represents alength of 2.79 microns.

FIG. 3 is an elevational cross-section of a frustoconical reactionapparatus in accordance with the present invention.

FIG. 4 is an elevational cross-section of a stripper column inaccordance with the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention relates to HMX and methods for making it,including some novel intermediates. In addition, the invention alsorelates to HMX compositions which may comprise other explosive ornon-explosive materials.

One synthetic scheme for preparing HMX involves production of theintermediates DAPT and TAT, as described in steps 1A, 1B, and 1C below.

Step 1A: Preparation of DAPT

Rather than dissolving hexamine in acetic acid, the hexamine is firstdissolved in room temperature (e.g., 22° C.) water (preferably 1 g waterper g hexamine), followed by addition of ice or a mixture of ice andwater (preferably 0.5 g per g hexamine). The resulting slurry is thenallowed to come to 0° C., followed by rapid addition of acetic anhydride(2 moles per mole hexamine). The resulting reaction is extremely rapid(about 1 minute in duration) and is evidenced by the melting of the ice.

One method of isolating the DAPT product can be accomplished in twostages. The first stage involves evaporation of the volatile components.Special care must be taken, however, to avoid the thermal instability ofDAPT when it is in the form of, for example, its diacetate salt.Therefore, the solution is heated to 40-45° C. to prevent cooling of thesolution caused by evaporation. A stream of flowing air is then passedover the solution. To evaporate the acetic acid selectively, the air issubstantially saturated with water vapor (e.g., at least 95% saturated),allowing the acetic acid to be preferentially evaporated. Theformaldehyde produced by the conversion of hexamine to DAPT is removedduring the evaporation of the water. Some polymerization of theformaldehyde occurs, resulting in an insoluble precipitate. Theevaporation is continued until the DAPT acetate salt begins toprecipitate.

The second stage of purification involves the removal of the polymericformaldehyde, as well as any remaining water and acetic acid. Whenapproximately ⅔ of the solution has been evaporated (at which point thebyproduct DAPT acetate salt has begun to precipitate), the reactionmixture is brought to 130-140° C. for a period ranging from 20-30minutes. The temperature must be raised above about 130° C. in order topromote depolymerization of the formaldehyde, as well as driving off anyremaining water or acetic acid. However, the temperature must not beallowed to rise above approximately 150° C., because DAPT will start todecompose at this temperature. The DAPT is then removed from the heatand air jet, and the system is cooled.

However, if the DAPT product is to be used in a subsequent reaction inwhich it is converted to TAT, and that subsequent reaction uses one ormore transition metal oxides as a catalyst, then the temperature of thereaction mixture can be as low as about 70° C. in the second stage ofpurification. This is because the transition metal oxide will catalyzethe depolymerization of formaldehyde polymers during the subsequentconversion to TAT. Therefore, in that situation, the temperature of thereaction mixture need not be increased to 130° C. or higher, becausedepolymerization of the formaldehyde polymers is not necessary at thatpoint.

Yet another way of isolating DAPT and removing volatile materialsinvolves the use of a stripper column. In general, in this embodiment ofthe process, the raw DAPT-containing product stream is fed to the upperhalf of a stripper column. A stream of hot gas (e.g., air at about 120°C. or greater) is fed to the lower part of the column, so that therising gas and the descending liquid come into countercurrent contact.Volatile materials in the liquid are vaporized and carried out of thestripper along with the gas stream. Apparatus suitable for use in thispurification technique is described in more detail below.

Without being bound by theory, it is believed than the relatively shorttime of contact between the DAPT and the hot gas in the stripper columnhelps avoid thermal degradation of the DAPT, and this permits the use ofgas at temperatures even greater than 120° C. In particular, therelative concentration of acetic acid decreases as it moves down thecolumn, and the DAPT tends to convert from salt to free base. Since DAPTas free base has greater thermal stability than its salts, contact withthe hottest gas near the bottom of the column will not cause substantialdegradation of the DAPT.

By the above-described synthesis process, nearly quantitative yields ofDAPT are obtained in a matter of minutes. The need to use excessreactant (acetic anhydride) to push forward equilibrium has beensubstantially diminished. The stoichiometry of the reaction requires 2moles of acetic anhydride per mole of tetraamine. A slight excess (e.g.,2.1 to 2.5 moles) of acetic anhydride can be used, if desired, but anessentially stoichiometric amount is generally sufficient and thereforepreferred.

The ice advantageously functions as a heat sink for the reactionexotherm. This enhances the product yield and shortens the reactiontime. The ice can be provided in any convenient form (e.g., cubes,chips, shaved ice, or slivers) but crushed ice is preferred because ofits high surface area and ready availability.

The reaction can be conducted in any appropriate reactor that providesefficient stirring, including reactors that are jacketed and equippedwith external cooling apparatus. The reaction yields are optimized bymaintaining the reactant mixture at a low temperature. The reactiontemperature is usually maintained between about −30° C. and 10° C., andis preferably maintained between about −15° C. and 0° C., mostpreferably at 0° C. (i.e., ice water conditions). Advantageously, theacetic anhydride is added to a pre-cooled (e.g., pre-cooled to at leastabout −10° C., more preferably to at least about −30° C.), stirredmixture of (a) tetraamine and (b) ice water.

Step 1B: Conversion of DAPT to TAT

The synthesis of TAT is accomplished by first converting DAPT into anester (see reaction 1 below), hydrolyzing the ester, and then reactingwith acetic anhydride (reaction 2). The ester can also be isolated orused as it is formed.

About 2.0-2.5 moles of acetic anhydride are used in reaction 1 per moleof DAPT. Preferably the temperature is kept below the reflux temperature(138° C.) initially, and after the initial exotherm, preferably thetemperature is kept at 110-120° C. until conversion of DAPT to the esteris complete.

The reactive ester is converted to TAT in the presence of water and atransition metal oxide catalyst, such as a mixture of copper oxide andiron oxide. Under these conditions, the reactive ester undergoeshydrolysis, resulting in the formation of a primary alcohol. The primaryalcohol is unstable in this environment, and it quickly decomposes,producing formaldehyde and a secondary amine. The secondary amine thenreacts with a second mole of acetic anhydride, giving the desired TATproduct. Reaction 2 shows this process.

Step 1C: Conversion of TAT to HMX

TAT can be converted to alpha-HMX by reaction with 98+% nitric acid andeither phosphorus pentoxide or dinitrogen pentoxide, at a temperaturebetween room temperature and about 40° C. Suitable procedures aredisclosed in Lukasavage U.S. Pat. Nos. 5,124,493 and 5,268,469, both ofwhich are incorporated herein by reference. Alternatively, TAT can beconverted to HMX as described below in steps 2C-2D, or 2E-2F.

A second synthetic scheme for producing HMX has also been invented. Thisprocess involves the use of a novel intermediate, acetyl acetatehexamethylene tetraamine (which is referred to herein as AAHT), thatcontains both an acetate group and an acetyl group. Unlike the syntheticroute to HMX that goes through DAPT, the acetate intermediate (AAHT)does not undergo hydrolysis (which would produce formaldehyde and asecond acetyl group), but instead can be isolated. This novelintermediate has the advantages of being more stable than DAPT and beingeasier to convert into TAT.

AAHT has the chemical formula shown below, with R being methyl.

This second synthetic scheme is described in steps 2A, 2B, 2C, and 2Dbelow.

Step 2A: Preparation of AAHT

Two processes have been developed for making AAHT. The first processcomprises reacting a hexamine/ice/water slurry with acetic anhydride attemperatures between −78° C. (which can be achieved, for example, byusing a dry ice/acetone bath) and −0° C., most preferably at about −30°C. Approximately 2 moles of acetic anhydride are added to the slurry permole of hexamine. The product of this reaction is AAHT. The reactionpreferably is conducted in a stainless steel or aluminum vessel equippedwith an efficient stirrer.

This method can be applied to synthesize any common derivative of AAHT,simply by varying the anhydride used; the reaction scheme describedabove is not limited to acetic anhydride. This general scheme is shownin reaction 3.

Optionally the ice can be pre-cooled to a temperature of −30° C. orlower, which will allow the use of less ice in the reaction.

The second method for making AAHT comprises reacting hexaminehexahydrate with approximately 2 mole equivalents of acetic anhydride attemperatures between −78 and −0° C., most preferably at about −30° C.AAHT is obtained as a waxy solid material.

Step 2B: Conversion of AAHT to TAT

TAT can be produced from AAHT by first forming the diester derivative ofAAHT. The diester has the general formula shown below.

To form the diester, about 2-4 moles of acetic anhydride are added permole of AAHT. This reaction mixture is then heated (e.g., to 110-120°C.) and stirred for a time sufficient to complete synthesis of thediester. Volatile components in the product mixture can be removed byevaporation, allowing isolation of the diester.

Alternatively, instead of recovering the diester, it can be converted toTAT in situ. The reaction mixture containing the diester is allowed tocool to a temperature between about 0-50° C., preferably to roomtemperature (about 22° C.), and transition metal oxide catalysts areadded, preferably iron and copper oxides. The formaldehyde generatedduring the course of the hydrolysis should be allowed to escape from thereaction mixture. About 2-4 moles water per mole of diester are thengradually added (e.g., over a period of about 90 minutes), at whichpoint the hydrolysis is complete. TAT is purified by heating to greaterthan 100° C. under an air jet, which evaporates the acetic acidbyproduct and any water that is coordinated to the TAT.

The conversion of AAHT to diester and then to TAT is shown in reaction4.

Step 2C: Conversion of TAT to SOLEX

An improved process has been discovered for preparing SOLEX(1-(N)-acetyl-3,5,7-trinitro-cyclotetramethylenetetramine) from TAT. Bylowering the temperature of the reaction mixture and by changing theorder of addition of the reagents used in prior methods, the amount ofnitrating agent required can be reduced significantly.

The preparation involves mixing TAT and low concentrations of nitratingagents, namely phosphorus pentoxide and nitric acid. (It should beunderstood that the TAT can be prepared, for example, by the procedureof step 1B or step 2B.)

TAT is added to nitric acid in a reactor. The nitric acid preferably isat a temperature between about 0° C. and 25° C., most preferably 10-15°C. The weight ratio of nitric acid to TAT preferably is at least about0.5:1, most preferably about 1.5:1. To this reactant mixture of nitricacid and TAT, phosphorus pentoxide is added slowly with stirring over aperiod of several hours. The reaction is strongly exothermic and thereaction temperature should be carefully monitored, and controlled ifnecessary, by slowing the addition of phosphorus pentoxide to thereactant mixture and/or by external cooling to prevent a potentiallydangerous exotherm from occurring. The reaction is normally completewithin a few hours (e.g. 3 hours). SOLEX is produced in essentiallyquantitative yields and high purity.

This method for preparing SOLEX is shown in reaction 5 (R is methyl inthis instance).

Another way of making SOLEX involves combining nitric acid andphosphorus pentoxide, preferably at a temperature of about 0-30° C.,then adding TAT to the reaction mixture. Preferably after the additionof TAT, the reaction mixture is kept at temperature no greater thanabout 68° C., more preferably no higher than about 45-55° C. Preferablythe weight ratio of nitric acid to phosphorus pentoxide is between about2:1 to about 4:1, more preferably about 3:1. The weight ratio of nitricacid to TAT preferably is at least about 1.875:1.

Step 2D: Conversion of SOLEX to alpha-HMX

A novel method for converting SOLEX to alpha-HMX involves a solid-statenitration reaction. That is, the SOLEX reactant is not dissolved in areaction solvent. Without being bound by theory, it is believed thatSOLEX is nitrated through an ion-exchange type interaction in the solidstate. SOLEX can be prevented from dissolving in, e.g., nitric acid byfirst loading the nitric acid with P₂O₅. In the new process, nitric acid(98+%) is placed into a reactor vessel, and the acid is cooled to about0-25° C., most preferably to about 15° C. Phosphorus pentoxide is addedslowly to the nitric acid with stirring. After the addition ofphosphorus pentoxide is complete, SOLEX is poured into the vessel,whereupon nitration begins immediately. Since the SOLEX does notdissolve in this reactant mixture, a solid-state nitration results.

The product can be purified and recovered by repeated washing andfiltration. Optionally, the filtrate can be treated with ammonia togenerate ammonium nitrate in either solid or liquid form, allowing arecycle loop. Yield of alpha-HMX is usually greater than 95% based onhexamine feed, preferably greater than 99%, most preferably greater than99.5%. Of the HMX in the reaction product, greater than 95% is the alphapolymorph, preferably greater than 99%, most preferably greater than99.5%.

The new method for alpha-HMX preparation is shown in reaction 6 (R ismethyl in this instance).

Steps 2C and 2D typically take a total of about 24-48 hours to complete.Because significant amounts of heat are generated, it is preferred toperform these reactions in a plastic (e.g., high density polyethylene)or metal (e.g., aluminum) vessel having a large surface area to enablethe heat to be readily dissipated.

Without being bound by theory, it is believed that the ability of theprocess shown in steps 2A-2D to produce pure (or nearly pure) alpha-HMXresults from the ability of SOLEX to form a unique crystal lattice, dueto the asymmetric nature of the molecule. The SOLEX can more easilyarrange in one polymorphic form because of its pendant acetyl group.

Instead of the procedures in steps 2C and 2D for converting TAT to SOLEXand then to HMX, the alternative procedures of steps 2E and 2F below canbe used.

Step 2E: Conversion of TAT to SOLEX

An initial reaction mixture comprising about 75% (by weight) nitric acidand about 25% phosphorus pentoxide is prepared, and TAT is immediatelyadded at a rapid rate. Detectable amounts of SOLEX are produced within10 minutes. (Pure SOLEX has a melting point of about 225° C.) Thereaction is exothermic, and cooling, such as by an external coolingjacket or external cooling coils, should be used to keep the temperatureof the reaction mixture below about 68° C., preferably between about45-55° C. Due to the very fast kinetics of this reaction, the conversionto SOLEX will usually be substantially complete within about two hours.Further conversion of SOLEX to HMX can be avoided by using aboutone-third more TAT than would be required for complete conversion of TATto HMX. Alternatively, if it is desired to allow the conversion toprocess all the way to HMX, stoichiometric amounts of the reactants canbe used.

Step 2F: Conversion of SOLEX to HMX.

Nitric acid and SOLEX are combined (preferably in a weight ratio ofabout 1.5-3.0, most preferably about 1.8), and then a first quantity ofphosphorus pentoxide is added. Preferably the weight ratio of the firstquantity of phosphorus pentoxide to SOLEX is about 0.25-2.0, mostpreferably about 0.7-0.8. After about 30 minutes, a second quantity ofphosphorus pentoxide can be added, and then after a further 30 minutes,a third quantity of phosphorus pentoxide added. The weight ratio of thefirst, second, and third quantities of phosphorus pentoxide can suitablybe about 4:1:1. A solid-state nitration of the SOLEX occurs, producingHMX in high yield. This reaction usually takes about two hours to besubstantially complete. (Pure alpha-HMX has a melting point of about281° C.)

In this process, preferably the SOLEX is dissolved in the nitric acid,so the reaction takes place in solution.

The HMX composition produced by this method has the useful property ofbeing easily converted to highly pure (e.g., greater than 99% by weight)beta-HMX. As long as the initial HMX composition has a melting point ofat least about 277° C., contacting it with a heated organic solvent(e.g., acetone at about 56° C.) will result in the production of thebeta polymorph.

In one embodiment of the process, the product is a mixture of variousHMX polymorphs.

The procedure of steps 2E and 2F takes much less time than steps 2C and2D (about four hours total versus about 24-48 hours). In addition, steps2E and 2F produce less acetyl nitrate byproduct, generate less heat, andrequire less surface area and/or heat resistance in the reaction vessel.

Optionally, step 2D or 2F can be followed by step 2G.

Step 2G: Recovery of Ammonium Nitrate.

After the nitration has proceeded to the desired extent (e.g., completeconversion to HMX, or alternatively, partial conversion that produces amixture of HMX and SOLEX), the reaction can be terminated by adding icewater to the reaction mixture, causing the product (e.g., HMX, SOLEX, ora mixture of the two) to precipitate. Filtration can then be used toseparate the precipitated product from the remaining aqueous solution.When filtered through a vacuum filter (or any other suitable filter),the product will be retained, and water and impurities will pass intothe filtrate. This filtrate, which will be a strong acid solution, canbe treated with ammonia to adjust its pH to about 4.0-6.0, preferablyabout 5.2-5.7. Water is then evaporated by heating it to at least 100°C., preferably to at least about 103° C. Phosphoric acid in the solutionwill remain liquid at these temperatures. Cooling the filtrate (e.g., toabout 70° C. or lower), will cause ammonium nitrate crystals to form.These crystals can be separated from the remaining liquid byconventional methods, and the recovered ammonium nitrate used forfertilizer or other known applications.

The product retained by the initial filtration is then preferably washedwith cold water. The wastewater from the cold water wash is a weak acidsolution. It can be treated by ion exchange or with activated carbon toremove impurities, allowing the purified water to be recycled.

This step not only minimizes the amount of waste products generatedduring the manufacturing of HMX, it also produces a highly pure ammoniumnitrate byproduct which its itself commercially valuable.

Alternatively, instead of recovering ammonium nitrate, after filtrationto remove the solid product, the remaining nitric acid can beconcentrated for recycle.

Some of the above-described chemical reactions are highly exothermic,and therefore care must be taken to control the temperature of thereaction mixture. This can be done by methods well known to personskilled in this field, using conventional and well-known equipment.However, it is also possible to conduct these reactions in a novelapparatus as shown in FIG. 3.

This particular embodiment of the reaction apparatus comprises afrustoconical vessel 10, which has a closed bottom 12 and an open top14. The vessel has an inner surface 16 and an outer surface 18. A liquidreaction mixture 20 is located in the vessel, in contact with the innersurface 16. An impeller 22 is mounted on a shaft 24, which can berotated by a motor 26, thereby stirring the reaction mixture. Anexternal cooling jacket 28 is wrapped around the vessel, in contact withthe vessel's outer surface 18. The jacket 28 can contain a heat transferfluid 30, such as water or Freon, to help remove heat from the vessel 10and thus from the reaction mixture 20. Enhanced heat removal can beprovided by increasing the speed of rotation of the impeller 22. Thecentrifugal force exerted on the liquid reaction mixture 20 by thisfaster rotation of the impeller causes the liquid to move outward and upthe inner surface 16 of the vessel, whereby the liquid surface takes onthe configuration shown by the dotted lines in FIG. 3. As a result ofmoving some of the liquid up the inner wall of the vessel, the liquid isplaced in contact with a greater surface area on the vessel's innersurface 16. As a result, the rate of cooling is increased.

In operation, the higher the rotational speed of the vessel 10, thehigher the liquid will be moved up along the inner surface of theimpeller, and the greater the rate of cooling. Therefore, by controllingthe speed of rotation of the vessel, the temperature of the reactionmixture can be controlled. One preferred way of implementing thiscontrol scheme is to place a temperature sensor, such as a thermocouple32, in the vessel 10, where it will contact the reaction mixture 20. Themeasurement made by this thermocouple can be transmitted via a wire 34to a computer 36. The computer can be operationally connected to themotor 26 that drives the shaft 24 and thus the impeller 22. As a result,when the temperature measured by the thermocouple 32 is higher than thepreset target temperature, the computer can increase the speed of themotor, thereby increasing the rotational speed of the impeller andmoving the liquid further up the inside walls. This increases thecooling rate (due to contacting the liquid with a greater surface areaon the cooled inner surface 16), and thus reduces the temperature of thereaction mixture 20. When the temperature has dropped to the desiredlevel, the computer can then slow down the impeller's rotation asneeded.

A further enhancement to this control scheme provides for situationswhere the reaction temperature increases beyond the point where it canbe controlled by the available cooling apparatus. If the thermocoupledetects that the temperature has exceeded a predetermined alarm level,the computer can then increase the speed of rotation of the impellerenough so that the resulting centrifugal force will expel apredetermined amount (e.g., 20% by weight) of the reaction mixture fromthe vessel, specifically by rising up the inner walls and going over thetop lip 38 of the vessel. This predetermined amount is chosen so thatits removal from the vessel 10 will bring the rate of heat generation bythe remaining reaction mixture 20 under control. A wide emergency catchpan (not shown in FIG. 3) can be located beneath the vessel, so that theexpelled reaction mixture will be contained, and yet will be spread outover a sufficiently large surface area that the reaction rate, and thusthe rate of heat generation, will be dampened.

The frustoconical reactor vessel 10 is preferably made of acorrosion-resistant thermoplastic polymer, such as high-densitypolyethylene or polypropylene. It could alternatively be made of metal,such as aluminum. The impeller 22 and shaft 24 can suitably be made ofthe same or similar materials. The walls of the cooling jacket cancomprise a thermoplastic polymer.

As mentioned above, in some of the process steps, water and volatileimpurities can be removed from a reaction product (i.e., from anitramine or nitramine intermediate) by passing a heated air stream overthe product. However, it is also possible to remove such volatilesubstances by means of a stripper column as shown in FIG. 4.

This separation technique makes use of a stripper column 50, whichpreferably is packed with saddles, rings, or other suitable packingmaterial 52 well-known in the art. A liquid stream 54 comprising thenitramine or intermediate (e.g., DAPT), water, and usually somerelatively volatile organic compounds, is fed into the column somewherein its upper half. A gas stream 56 that comprises (and preferablyconsists essentially of) air is fed into the column somewhere in itslower half. The gas stream has a temperature of at least about 120° C.,and optionally can have a temperature as high as 200° C. or even higher.The gas and liquid streams are contacted in counter-current fashionwithin the column, whereby a substantial percentage of the water andvolatile organics that are present in the liquid feed stream 54 areremoved into the gas phase. A bottoms stream 58 is drawn from the columnthat contains the nitramine or intermediate (e.g., DAPT) and relativelylittle water (e.g., less than 10% by weight, preferably less than 5%,most preferably less than 1%). An overhead stream 60 is also drawn fromthe column, and comprises air, water vapor, and vaporized organiccompounds such as formaldehyde and acetic anhydride, and possible alsosome entrained liquid.

This technique of using a stripper column allows the use of much hottergas streams than can be used when the gas is merely passed over thesurface of a pool of the liquid, while still avoiding or minimizing anydegradation of the nitramine or intermediate. Therefore, this techniquespeeds the drying of the of the desired product. This approach isparticularly useful for drying a DAPT-containing liquor, which canotherwise form a bottleneck in the overall manufacturing process.

The alpha-HMX generated in the above-described processes has a uniquecrystalline or particulate form consisting of long fibers. Without beingbound by theory, it is believed that in some instances, the alpha-HMXparticles take the form of elongated, flat sheets that roll up to formtubules having water trapped therein. Whether the particles are hollowor not, they generally are in the form of elongated fibers or rods,having an aspect ratio (length:diameter) of at least about 100:1, oftenas high as 1,000:1. The novel structure can be seen in FIG. 1, ascontrasted to the material in FIG. 2 that was made by a prior artprocess.

If desired, alpha-HMX can be converted into the beta-form by simplydissolving α-HMX in suitable organic solvent, providing beta-HMXcrystals therein, and then evaporating the solvent. Examples of suchsolvents include acetone, cyclohexane, and a mixture of 20% by weightgamma butyrolactone and 80% acetone.

The alpha-HMX produced as described above has a relatively low bulkdensity, due to the small diameter and large aspect ratio of thefiber-like particles. This low bulk density makes it difficult to placethe material into pressing fixtures. Also, because of the fiber-likestructure of the particles, even after being pressed, the bulk densitytends not to be close to the maximum theoretical density.

The HMX produced as described herein can be manipulated in several waysto produce useful mixtures, granules, and/or shaped articles that canoptionally comprise one or more additional materials. Thesemanipulations can increase the density, structural strength, explosivepower, or other properties of the composition. One such manipulation isto coat alpha-HMX particles with a second material. The term “secondmaterial” is used generically herein to refer to materials (or mixturesof materials) other than alpha-HMX that can be combined with it invarious ways. Examples of second materials that can be sorbed ontoalpha-HMX include RDX, beta-HMX, TNT, ammonium nitrate, aluminum,lithium hydride, and lithium aluminum hydride.

For instance, a first set of alpha-HMX particles can be coated with asecond material by sorbing that material on the HMX particles. A secondset of alpha-HMX particles can be coated with a second material that isdifferent from the one used to coat the first set of particles. The twosets of coated particles could then be mixed, and pressed into a shapedarticle. Alternatively, the two sets of coated particles could be madeinto separate articles or granules, which could then be combined in asingle casing.

As yet another alternative, an article or granule made from HMX orcoated HMX, which has void spaces therein, can have a second material(or a mixture of such materials) sorbed into those void spaces, and/orsorbed onto the surface of the article or granule.

It would also be possible to sorb multiple layers of different materialsonto a HMX-containing particle, granule, or article. The differentlayers could have, for example, different density, electricalconductivity, etc. The different layers could also be mixtures of HMXwith different second materials. Persons skilled in the art willappreciate that these techniques can be used in myriad combinations toproduce various particles, granules, and/or shaped articles thatcomprise at least one second material in addition to alpha-HMX. Suchparticles, granules, and/or shaped articles will be referred tocollectively herein as “HMX products.”

One type of HMX product that is especially useful is a granule or shapedarticle that comprises, and preferably consists essentially of,alpha-HMX and aluminum. The latter provides a large quantity of heatwhen oxidized, and thus can be highly useful as part of an HMX product.

The alpha-HMX produced as described herein is especially well suited formixing with aluminum powder, because its unique particulate form allowsthe ready formation of a highly homogenous mixture. In contrast, priorart beta-HMX tends to form a relatively heterogeneous mixture withaluminum powder, thus degrading the explosive power of the beta-HMXrather than enhancing it.

Although a wide variety of aluminum concentrations can be used in suchmixtures with alpha-HMX, aluminum concentrations of 0.1-20% by weightare usually preferred. One particularly preferred mixture comprisesabout 7% aluminum having an average particle size of about threemicrons. Such a mixture of HMX and aluminum can be granulated or pressedinto a shaped article, as described above.

One highly attractive feature of such HMX products that comprisealuminum or some other second material is their structural integrity andstrength. Such products can be formed into any desired shape (e.g., aright cylinder, a sphere, or a hollow cone) without the use of aseparate binder, which would tend to dilute the energetic properties ofthe HMX. Although it may be useful to add a small amount of graphite(e.g., less than 1% by weight) to aid in handling, no binder should berequired.

One particular method for increasing the bulk density of alpha-HMXinvolves treating alpha-HMX particles with a small amount of organicsolvent (e.g., about 0.3-2.5 g of solvent per g of HMX, preferably about0.4-0.85 g/g) which at significantly high temperatures (e.g., about 110°C. or higher, preferably about 110-150° C.) dissolves a relatively highmass of HMX per unit mass of solvent. Suitable solvents include gammabutyrolactone, other lactones, acetone, lactams, formamides, TMF,sulfoxides, and fluorocarbons (e.g., Freons). The quantity of solvent isintentionally restricted so that it will dissolve only a fraction (e.g.,no more than about 10-20% by weight) of the total HMX so treated. Theliquid containing the dissolved portion of the HMX fills at least someof the areas between the remaining undissolved fibers of the alpha-HMX.When the solvent is evaporated, the HMX that had been dissolved is thenprecipitated out, filling at least some of the voids between thealpha-HMX fibers with solid crystals.

Optionally, seed crystals of another polymorph of HMX can be present(e.g., beta-HMX). The seed crystals can be supplied by small amounts ofother HMX polymorphs that may inherently be present as impurities inalpha-HMX. For example, as little as about 1% by weight (or even less)of beta-HMX in a composition that is predominantly (e.g., greater thanabout 99%) alpha-HMX can be sufficient.

It is also possible to make fine particles of beta-HMX. For example,Class 5 beta-HMX can be made by dissolving HMX (that has been made asdescribed herein) in a solvent such as boiling acetone, and then spraydrying using conventional spray drying equipment, e.g., at a temperatureof about 50° C.

Without being bound by theory, it is believed that this process forproducing fine beta-HMX works well because of the very high purity ofthe HMX used as the starting material. Class 5 beta-HMX is especiallyuseful as a rocket propellant, and can be made using this technique muchless expensively than by the conventional processes for direct synthesisof beta-HMX.

Alpha-HMX particles can be agglomerated into granules having increasedbulk density. In particular, the low-density alpha-HMX fibers can beconverted to high-density granules, which are suitable for pressing intoshaped charges and other durable shaped articles. Finished pressedarticles may be prepared from such granules with a very high percent ofthe theoretical maximum density. No binders or additives of any kind arerequired.

After drying the alpha-HMX, the mass of material is broken down intoparticulates having a desired size distribution. The desired sizedistribution can be effected by passing the starting material through asieve. The sieved particulate material is then “dry stirred.” This ispreferably done by stirring the particulates in a circular motion in thepresence of a small amount (e.g., 0.001-0.5 g of solvent per g of HMX)of additional solvent that helps fluidize the entire mass. The quantityof solvent is less than what would cause the material to cake, becausecaking would prevent the fluid motion of the particles. A plurality ofparticulates agglomerates to form a granule. In general, the smaller theparticulates, the smaller the granules that will be formed. Thefluidized motion of the solvent dampened particles causes the furthercompaction and rounding of each granule. During the stirring process,additional small amounts of solvent may be added to the moving bed ofmaterial, further softening the material and assisting the dynamicactions which promote the formation of generally spherical HMX granuleshaving increased bulk density. This process preferably is carried out bycirculating the sieved material in a circular or elliptical channel in avessel, so that centrifugal force helps cause the particles toagglomerate into denser granules. These granules are porous andpermeable. Therefore, one or more second materials can be sorbed intothe granules. It is also possible to coat the exterior of a granule withone or more second materials. Further, a plurality of granules can beformed into an article having any desired shape, for example bypressing. The alpha-HMX granules in combination with one or more secondmaterials will form an article that will retain its shape under normalhandling, without the need for any binder or adhesive.

HMX, and compositions containing HMX together with other materials, havemany uses as explosives or propellants. For example, the oil industryuses HMX as an explosive in shaped charges for the perforation of wellcasings. Apparatus and techniques for using such shaped charges forperforation are well known. Examples of such perforation equipment andtechniques are described in the following Schlumberger U.S. patents,each of which is incorporated here by reference: U.S. Pat. Nos.5,911,277; 5,673,760; 5,597,974; 5,505,134; and 5,355,802.

The various aspects of the present invention can be further understoodfrom the following examples.

EXAMPLE 1 Preparation of DAPT

An open-top, 8-quart stainless steel pot equipped with an efficientmechanical stirrer is charged with 980 grams (7 moles) of hexamine.Water (980 grams) is added to dissolve much of the hexamine. Thishexamine/water slurry is cooled to approximately 0° C. To this, 490grams of ice are then added. Acetic anhydride (530 grams, slightly morethan 2 moles) is then poured into the reaction vessel with rapidstirring over a period of about 30 seconds. The reaction is evidenced bythe rapid melting of the ice in the reaction mixture. The reaction isfinished within a minute or so after the acetic anhydride is added, andthe product is ready for recovery and/or purification.

Purification of the product can be accomplished by passing steam overthe reaction product in the reaction vessel. This heats the material andcauses the acetic acid by-product to evaporate. Another by-product, aformaldehyde polymerization by-product, is also formed. To remove thispolymer by-product and any remaining water, acetic acid, or othervolatile material, the reaction mixture is heated to 130-140° C. for20-30 minutes. The product is then cooled. DAPT can be isolated andrecovered at this point by filtration, washing, and drying. The typicalyield is 65-100%.

EXAMPLE 2 Conversion of DAPT to TAT

To 1482 g of cooled and purified DAPT, 1570 grams of acetic anhydride isadded with rapid stirring. Careful control of cooling must be maintainedin order to keep the system below reflux temperature (138° C.). Afterthe initial exotherm, the temperature is kept at roughly 110-120° C. for2 hours. Conversion of DAPT to the ester intermediate (having threeacetyl groups in addition to the one ester group) is complete at thispoint.

Conversion of the ester to TAT (i.e., the tetraacetyl derivative) isaccomplished by the addition of a catalytic amount (preferably less thanfive mole percent) of transition metal oxides, and the addition of 126grams (7 moles) of water. A combination of copper oxide and iron oxideis preferred for use as a catalyst in the reaction. The copper can beadded in the form of copper wire, while the iron can be added in theform of steel wool. More water (1 mole per mole of hexamine in the DAPT,as opposed to isolated hexamine) is then added to the reaction mixtureover a period of approximately 90 minutes. The temperature is thenincreased to 130-140° C. for 20-30 minutes, driving off any residualacetic acid, any remaining water, and other volatiles. The esterfunctionality is hydrolyzed, generating a primary alcohol and aceticacid. The alcohol quickly decomposes to generate formaldehyde, whichleaves the reaction mixture as a gas. The product formed is a secondaryamine, which then reacts with a second mole of acetic anhydride to formTAT.

TAT is isolated by placing the system in a rapidly flowing stream ofair, with heating, which causes the volatile components to be removed.Once all volatile components have been removed, the temperature of thesystem will rapidly rise and should be allowed to reach 140-150° C. Theheat is then removed from the system, but airflow should remain on, inorder to cool the system. Once the system reaches 70-90° C., acetoneshould be added (enough to increase the volume by about 20%), followedby a few milligrams of seed TAT crystals to facilitate crystallization.The crystallized product is then filtered, and washed with cool acetone.The crystalline product is then dried at 100° C. (removing any remainingwater), and stored in an airtight container to prevent absorption ofwater. A quantitative yield of product is recovered as a solid.

EXAMPLE 3 Preparation of AAHT

Hexamine is dissolved in a minimum of water (1:1 molar ratio) which isthen cooled to ≦10° C. A mass of ice equal to ⅓ the mass of hexamine ispre-cooled to about −30° C. This is then mixed with the pre-cooledhexamine solution, creating a slurry. To this slurry, 2 mole equivalentsof acetic anhydride (also pre-cooled to −30° C.) are added. AAHT isformed within a minute, as is evidenced by the immediate melting of theice, illustrating the exothermic nature of this reaction.

Purification of AAHT is accomplished by heating the reaction vessel to atemperature above 130° C. in the presence of flowing air. This has theeffect of driving off all volatile components, leaving the AAHT. Theevaporation optionally can be done in a two-stage evaporation, asdescribed above for recovery of DAPT. The AAHT can be isolated at thispoint or the synthesis can continue.

EXAMPLE 4 Alternative preparation of AAHT

AAHT can also be produced utilizing hexamine hexahydrate (referred tohereafter as hex-hex). One mole of hexamine is placed into 6 moles ofwater at room temperature. This mixture is then cooled to approximately−30° C., forming hex-hex, a waxy solid that can be isolated and is quitestable.

For AAHT synthesis, a quantity of hex-hex is cooled to −30° C., followedby the addition of slightly more than 2 mole equivalents anhydride. Theanhydride is also pre-cooled to approximately −30° C. before addition.There is a slow onset to the reaction, until it reaches approximately−15° C. at which point a rapid rise in temperature occurs, bringing thereaction to approximately 40-50° C. Purification is accomplished in thesame manner as in Example 4.

EXAMPLE 5 Conversion of AAHT to TAT

Three moles of acetic anhydride are added per mole of AAHT, and thereaction mixture is then heated to 110-120° C. and stirred for 2 hours,completing synthesis of the diester. Removal of volatile components byevaporation allows isolation of the diester.

Alternatively, instead of recovering the diester, it can be converted toTAT in situ as follows. The reaction mixture containing the diester isallowed to cool to room temperature (about 22° C.), and iron and copperoxide catalysts are added in the form of steel wool and copper wire.Special care must be taken to leave the reaction vessel uncovered sothat the formaldehyde generated during the course of the hydrolysis canescape. Two moles water per mole of diester are then added over a periodof about 90 minutes, at which point the hydrolysis is complete. Theproduct, TAT, is purified by heating to 130-150° C. under an air jet fora period of approximately 20 to 45 minutes, which evaporates the aceticacid byproduct and any water that is coordinated to the TAT. The typicalyield is 90-100%.

EXAMPLE 6 Conversion of TAT to SOLEX

To generate 100 grams of SOLEX, 150 grams of nitric acid (a five-foldreduction over the prior art method) is placed into an aluminum orplastic reactor. The reactor temperature is adjusted to 15° C.Crystalline TAT (100 grams) is slowly added to the reaction vessel withefficient stirring. After the TAT has dissolved into the nitric acid, 24grams of phosphorus pentoxide is added. Care is taken to insure that therate of stirring is sufficient to prevent clumping of the reagents;clumping can cause localized overheating, a potential hazard. Thereaction is then stirred for about 1 hr, at which point 8 additionalgrams of phosphorus pentoxide is added. Time lapses between additions ofphosphorus pentoxide allow the heat of reaction to dissipate. Theaddition is repeated two more times, until a total of 48 grams ofphosphorus pentoxide has been added. This is a dramatic decrease in theamount of phosphorus pentoxide required by prior methods. The reactiontemperature is kept between 20-25° C. during the course of the reaction.After the addition of phosphorus pentoxide is complete, the reaction isstirred for approximately 5 hours until the reaction mixture begins togel. At this point, the reaction is nearly finished and the reactionmixture is transferred to a temperature-controlled container and allowedto stand for 24-48 hours at room temperature. Purification isaccomplished by filtering the material and washing it with copiousamounts of hot water. The result of this process is a nearlyquantitative yield of pure SOLEX.

EXAMPLE 7 Alternative conversion of TAT to SOLEX

First 562.5 g of P₂O₅ are dissolved in 1,125 ml of nitric acid. Next 500g of TAT are added in four increments of 125 g each, with 30 minutesbetween each addition of TAT. The reaction mixture is maintained atabout 30-45° C., preferably at about 37° C. The typical yield of SOLEXis well in excess of 90% (e.g., about 96%).

EXAMPLE 8 Conversion of SOLEX to alpha-HMX

To prepare 100 grams of HMX, 100 ml of nitric acid is added to analuminum or plastic reactor. The contents of the vessel are cooled toapproximately 15° C. 80 grams of phosphorous pentoxide are slowly addedwith stirring to the reactant mixture in the vessel, resulting in atemperature increase due to the exothermic formation of dinitrogenpentoxide. The rate of addition should be monitored to allow no morethan a 10-20° C. increase in temperature. After the addition of thephosphorus pentoxide, the reaction vessel should be cooled to 10-20° C.After the addition of the phosphorous pentoxide is complete, 100 gramsof SOLEX is rapidly stirred into the mixture, generating a viscousslurry. Care needs to be taken to ensure that the entire mixture iscooled, which is necessary to avoid the possibility of a fume-off. Themixture will continue to thicken during this time, so the mixture shouldbe transferred to an aging container that has enough cooling surface topermit cooling without stirring. The mixture immediately begins tothicken. The reactant mixture is then transferred to a suitablecontainer having temperature control apparatus.

After aging for 24-48 hours, at room temperature, the reacted materialis filtered and washed several times with fresh (deionized) hot water ina vacuum filter. This process should be repeated several times in orderto insure complete purification. A quantitative yield of high purityalpha-HMX is obtained as a solid.

EXAMPLE 9 Alternative conversion of SOLEX to HMX

First, 600 g of SOLEX are dissolved in 1,091 ml of nitric acid. To thismixture, 436.3 g of P₂O₅ are added. After waiting 30 minutes, another109.1 g of P₂O₅ are added. After waiting another 30 minutes, another109.1 g of P₂O₅ are added. The temperature of the reaction mixture ismaintained at about 30-45° C., preferably at about 37° C. The reactionis complete within about five hours, and the yield of HMX is usuallyabout 95% or greater.

EXAMPLE 10 Conversion of alpha-HMX to beta-HMX

The HMX product of Example 9, after being washed with water and dried,is a fluffy powder having a melting point of at least about 277° C. To100 g of this HMX are added 300 ml of acetone at a temperature of about56° C. The HMX converts to beta-HMX within about five minutes.

EXAMPLE 11 Adsorption of substrate onto alpha-HMX

TNT is dissolved in ethyl acetate or some other solvent. Either thesolvent should be one in which HMX will not dissolve, or else thesolvent should be substantially pre-saturated with TNT. The TNT solutionis then contacted with alpha-HMX made as in Example 8. Drying causes theTNT to form a thin film or coating on the HMX. The amounts of TNT andHMX used can vary widely, but can suitably be, for example, 1:1 ratio byweight.

EXAMPLE 12 Granulation of alpha-HMX

A quantity of alpha-HMX (400 g) is treated with a mixed solvent (235 gof 20% gamma butyrolactone, 80% acetone). To the resulting paste isadded with stirring a small quantity (1.6 g) of fine beta HMX seedcrystals. The stirring is not elaborate and is complete in a fewminutes. The resulting paste is placed as a shallow layer into a pan andthe pan is placed in an oven at about 120-130° C. The paste is removedwhen dry in about 20 minutes. The dried paste is broken up and passedthrough a screen, e.g., a #14 sieve. The resulting powder is transferredto an agitator consisting of a cylindrical chamber with a stirrer orimpeller. The particles are stirred so the whole bed is in motion and isflowing, fluidized but not violently so, and as the mixture is flowing asmall amount of the solvent (e.g., 0.05 g of solvent per g ofparticulates) is added. The quantity of solvent is limited only by thefact that too much (e.g., about 10 g) will cause the particles to cake.The break point between acceptable and excessive amounts of addedsolvent is rather sharp (e.g., plus or minus a few drops of solvent).The material is treated in this manner for a few minutes, after whichthe material is removed from the agitator and dried in an oven at about90° C.

EXAMPLE 13 Crystallizing beta-HMX in alpha-HMX voids

HMX prepared as in Example 9 is dissolved in a solvent such as acetone.This solution is contacted with porous alpha-HMX particles made as inExample 8. Evaporation of the solvent causes crystallization of beta-HMXin the void spaces in the alpha-HMX particles.

The preceding description of specific embodiments of the presentinvention is not intended to be a complete list of every possibleembodiment of the invention. Persons skilled in this field willrecognize that modifications can be made to the specific embodimentsdescribed here that would be within the scope of the present invention.

What is claimed is:
 1. A process for making HMX, comprising the stepsof: (a) combining SOLEX and nitric acid, thereby forming a reactionmixture; and (b) adding phosphorus pentoxide to the reaction mixture,whereby a solid-state nitration reaction produces a product thatcomprises HMX, the product having a melting point of at least about 277°C.
 2. The process of claim 1, further comprising stopping the reactionby cooling the reaction mixture.
 3. The process of claim 2, wherein thereaction mixture is cooled by addition of ice.